With ever-increasing demand for wireless communication and broadband services, there is an ongoing evolution of Third Generation (3G) and Fourth Generation (4G) cellular networks like High Speed Packet Access (HSPA), Evolution-Data Optimized (EV-DO), Long Term Evolution (LTE), Worldwide Interoperability for Microwave Access (WiMAX), International Mobile Telecommunications-Advanced (IMT-Advanced) (e.g., LTE Advanced), etc., to support ever-increasing performance with regard to capacity, peak bit rates and coverage. In case of a mobile communication environment, such as Third Generation Partnership Project's (3GPP) LTE network, the Evolved Universal Terrestrial Radio. Access (EUTRA) or Evolved Universal Terrestrial Radio Access Network (E-UTRAN) air interface for LTE may support wireless broadband data service at a rate of up to 300 Mbps in the downlink (DL) and 75 Mbps in the uplink (UL).
In traditional wireless communication systems, radio signals are not being transmitted and received on the same frequency at the same time. The main hindrance in simultaneous transmission and reception (also known as “full duplex” communication) is that broadcasted radio signals are attenuated rapidly over distance, causing a drastic difference in transmitted and received signal power levels such that, during such simultaneous transmission and reception, the received signal by a wireless unit is often overshadowed by the unit's own transmitted signal during analog-to-digital conversion. Such “self-interference” is especially true for macro cellular communication systems where the distance between two wireless units is large (so that a unit wishing to perform simultaneous transmission and reception may encounter significant self-interference). As a result, uplink and downlink transmission resources are typically divided either in frequency, as in Frequency Division Duplex (FDD), or in time, as in Time Division Duplex (TDD) communications. Such division in radio resources is also typically fixed for the entire network to avoid mutual interference between the bi-directional communications.
However, as wireless data communications become increasingly popular, it is anticipated that significantly denser deployment of wireless access nodes or base stations will be required in the future to cope with the exponential growth in data traffic. As the distance among access nodes reduces, the relative power difference between the transmitted and received signals at any access node also reduces significantly. In this case, full-duplex radio communications (i.e., simultaneous transmissions and receptions) may be feasible with the use of certain self-interference cancellation techniques. This is especially true for device-to-device communications (versus communications between a wireless device and its access node or base station), which is expected to play a major role in future radio access. It is also true in a super-dense cellular network where over-provisioning of radio resources is achieved through numerous short-range, low-power access points over a large bandwidth available at a high frequency range (e.g., the mini-meter wave range of 30-100 GHz).
It is observed here that the potential gain in spectral efficiency provided by full duplex communications is substantial over FDD and TDD communications because the total available radio resources need not be divided. The potential benefits of full-duplex communication to a wireless network has been evaluated and analyzed in P. C. Weeraddana, M. Codreanu, M. Latva-aho, and A. Ephremides, “The Benefits from Simultaneous Transmission and Reception in Wireless Networks,” Proc. 2010 IEEE Information Theory Workshop, Dublin.
In M. Duarte and A. Sabharwal, “Full-Duplex Wireless Communications Using Off-The-Shelf Radios: Feasibility and First Results,” Proceedings of Asilomar Conference on Signals, Systems, and Computers, 2010 (hereafter “Paper-1”), it was proposed that the self-interference from the transmitted signal may be suppressed at the receiver using an analog cancellation circuitry at radio frequency and/or a digital cancellation module at baseband frequency. Both of these cancellation techniques try to subtract the known transmitted signal from the received signal.
In J. Choi, M. Jain, K. Srinivasan, P. Leis, and S. Katti, “Achieving Single Channel, Full Duplex Wireless Communication,” Proceedings of MOBICOM 2010, pp. 1-12, 2010 (hereafter “Paper-2”), it was proposed that, in addition to the analog and digital cancellations mentioned above, two transmit antennas and one receive antenna may be placed at fixed, preset locations in such a way that the receive antenna is located at a null position where the two radio signals transmitted from the two transmit antennas are added destructively.